In the coatings industry, differently modified polysiloxanes have long been used as additives in coating material compositions such as paints and varnishes, and also in molding compounds. In general these are polymers which possess a polysiloxane backbone grafted for example with polyester and/or polyether (side) chains. Also used, for example, are linear block copolymers, which as well as polysiloxane blocks also include polyether and/or polyester blocks. As a result of these modifications, various advantageous performance properties are generated, and/or compatibility is achieved between the additive in question and the corresponding coating material compositions or molding compounds. The polyether-modified and/or polyester-modified polysiloxanes are, in general, surface-active additives, in other words additives which can—often through a controlled accumulation at the surface of the respective coating—lead to particular advantageous surface properties. Examples of such properties include effective flow of the coating material compositions. Examples of properties of the coatings or finishes produced from the coating material compositions, or of the corresponding moldings, include a high scratch resistance or else a low slip resistance and good antistick properties in the case of soiling (in other words, effective dirt repellence) in conjunction with effective recoatability. Especially advantageous, accordingly, is the attainment of a balance between low slip resistance and/or effective dirt repellence, on the one hand, and effective recoatability, on the other. A balance of this kind is of great importance, for example, if already coated substrates or moldings are to be temporarily stored, in order then to be subsequently available directly for direct further processing or further coating. One of the reasons why this balance is important is in order, in particular, to be able to repair, for example, a dirt-repellent finish as described above, more particularly a topcoat finish, in the event of damage, without experiencing adhesion problems—in other words, to be able to repaint damaged and possibly abraded areas without problems of adhesion. Such damage may occur locally as a result of direct mechanical exposure of a painted surface. The damage may of course also come about as part of continuous wear in everyday use or everyday exposure, in which case a complete renewal or recoating of the original coatings is usually required. In this latter case specifically, the described balance is very important.
A problem and a disadvantage is that the modified polysiloxane additives known for use in coating material compositions and molding compounds usually have an unsatisfactory stability and/or exhibit migration behavior. Under the influence of thermal energy or heat, in particular, the polyether-modified and/or polyester-modified polysiloxanes do not have satisfactory stability, and may degrade. This is especially true of the polyether-modified polysiloxanes. The reaction products formed on such degradation, especially the resultant silicone oils, are in general incompatible or poorly miscible with the other constituents of the coating material composition or molding compound or of the polymeric matrix of the existing coating or existing molding, and in that case exhibit uncontrolled migration to the surface of the coatings or the molding. The usual outcome manifested is that of surface defects such as craters and popping marks, for example (see, for example, Steven J. Hinder et al., “Migration and segregation phenomena of a silicone additive in a multilayer coating”, Progress in Organic Coatings, 54 (2005) 104-112). Another problem arises, moreover, in terms of the recoatability of the coating produced. As a result of the uncontrolled accumulation on the surface, appropriate recoatability and intercoat adhesion no longer apply. This effect is specially relevant for thermally curing coating material compositions and molding compounds, especially for thermally curing coating material compositions and molding compounds which are cured at high temperatures. This effect is likewise relevant, for example, for coatings which after having been produced, have been exposed to correspondingly high temperatures in the course of their applications. Examples include certain powder coatings, coil coatings, can coatings, or enamels for electrical insulation.
Despite the fact that the polyester-modified polysiloxanes of the kind described, for example, in EP 0175 092 B1, EP 0217 364 B1, and U.S. Pat. No. 7,504,469 offer advantages over the polyether-modified copolymers in terms of thermal stability, the thermal stability continues to be inadequate and to be in need of further improvement. An additional factor is that the modified siloxanes described, in other words the polyether-modified polysiloxanes and in particular the polyester-modified polysiloxanes as well, may exhibit a tendency toward migration even without the explicit influence of high temperatures on the coating material compositions and/or on the finishes produced from them. This means in particular that, over time, the additive may accumulate continuously at the surface of an existing coating film, or may even emerge from the surface of the coat. This effect may be exacerbated, of course, in coatings exposed to particular temperature fluctuations and/or to temperatures temporarily increased again and again, examples being automobile finishes (such as the finishes in the area of the hood, which are exposed to the heat of the engine).
The effects described are also highly relevant, in particular, in the context of the coil coating process, in which the coated strip is rolled up again and stored. Because of the internal pressure in the roll, acting on the coating, the migration behavior is exacerbated again. The same also applies in respect of painted substrates which, while having not been coated by the coil coating process, are nevertheless stored in stacked form, for example, and hence likewise subject to a high pressure. As a result of the migration, damage may possibly arise in the finish and there may also be adhesion problems, with respect to the intercoat adhesion, for example. Moreover, the emergence of the additive from the surface can lead to deposition of the additive on the reverse of the coated and rolled-up strip, and this can lead to defects and adhesion problems in the event of subsequent coating of the reverse of said strip. In any case, therefore, the longevity of the additives and hence of the advantageous effects they produce is inadequate and therefore deserving of improvement. Equally deserving of improvement is the migration behavior, described as emergence of the additive. Continuous migration additionally plays an important part in the case of coatings for substrates which are used in the food industry, for example, as containers or packaging. For instance, the migration and the emergence of the polymers from the varnish film may prove to be highly deleterious in the context of internal can coating for preserves.
As further modified polysiloxane block copolymers, polysiloxane-polyoxazoline copolymers, for example, are known. As well as polysiloxane blocks they also comprise polyoxazoline blocks, these being blocks prepared by polymerization of oxazolines (dihydrooxazoles), more particularly 2-oxazolines (4,5-dihydrooxazoles). EP 0 756 859 A1, EP 0 640 643 A2, and also U.S. Pat. No. 4,659,777 describe the use of such block polymers in haircare and cosmetics products or else in textiles, or in certain textile fibers.
U.S. Pat. No. 4,659,777 A also discloses the use of the additives described therein in compositions which are not thermally curing. Taught in particular is their use in thermoplastic and hence not thermally curing compositions such as polyvinyl chloride (PVC). In column 5 lines 17 ff., of U.S. Pat. No. 4,659,777 A, it is noted that the block copolymers described therein, when blended with other polymeric materials, pass by migration to the surface of the material in question. In this case there is a reorientation of the block copolymers at the surface, leading to a lowering of the contact angle for polar liquids and hence to relatively hydrophilic surfaces. Migration and reorientation are therefore essential to the effects addressed in U.S. Pat. No. 4,659,777 A. In thermally curing and hence crosslinked systems, however, such migration and reorientation of polysiloxane-polyoxazoline copolymers is very largely prevented, and so the effects described as essential in U.S. Pat. No. 4,659,777 A cannot be transposed to thermally curing systems.